Method for manufacturing 6xxx alloy materials for vacuum chambers

ABSTRACT

The invention relates to a manufacturing process for an aluminum block of at least 250 mm thick designed for the manufacture of elements for vacuum chambers in which the following operations are carried out successively: an alloy block is cast by semi-continuous casting, the composition of this block in weight % being: Si 0.5-1.5; Mg: 0.5-1.5; Fe&lt;0.3; Cu&lt;0.2; Mn&lt;0.8; Cr&lt;0.10; Ti&lt;0.15, other elements &lt;0.05 each and &lt;0.15 in total, the rest aluminum; solution heat treatment is performed at a temperature ranging between 450 and 560° C. directly on the cast block and optionally homogenized; the block that has undergone solution heat treatment is quenched at a cooling speed between the solution heat treatment temperature and 200° C. of at least 200° C./h; the block quenched and optionally stress-relieved is artificially aged. The blocks obtained in this way are advantageous for the production of vacuum chambers for the manufacture of integrated electronic circuits containing semiconductors, flat screens and/or photovoltaic panels.

FIELD OF THE INVENTION

The invention relates to the manufacture of 6xxx alloy products, in particular designed to be used in the production of vacuum chambers for the manufacture of integrated electronic circuits containing semiconductors, flat screens and photovoltaic panels.

BACKGROUND OF RELATED ART

In the manufacture of aluminum alloy blocks designed to be used in the production of vacuum chambers for the manufacture of integrated electronic circuits containing semiconductors, flat screens and photovoltaic panels, it is important to obtain a set of properties, while limiting the cost of operations.

The blocks must first of all have satisfactory mechanical characteristics to allow machine production of parts of the required dimensions and rigidity in order to be able to obtain a vacuum generally at least of the level of the average vacuum (10⁻³-10⁻⁵ Torr) without bending. The required ultimate tensile strength (R_(m)) is therefore generally at least 260 MPa and even more if possible. In addition, residual stresses in blocks designed to be bulk machined must be low in order to obtain the required dimensions without difficulty and without bending due to machining. As the dimensions of vacuum chambers are continuously increasing, in particular for the production of liquid crystal screens or large size photovoltaic panels, it is necessary to produce increasingly thick aluminum alloy blocks, in particular at least 250 mm or even 300 mm thick. The thicker the blocks are, the more it is difficult it is to obtain adequate mechanical properties while maintaining excellent stability during machining.

The level of porosity of the blocks must in addition be sufficiently low to obtain a high vacuum (10⁻⁶-10⁻⁸ Torr) if required. In addition, the gases used in vacuum chambers are frequently very reactive and in order to avoid the risks of pollution of the silicon wafers or liquid crystal devices by particles or substances coming from the walls of the vacuum chambers and/or frequent part replacement, it is important to protect the surfaces of the chambers. Aluminum proves to be an advantageous material from this point of view because it is in general possible to produce a hard anodized oxide coating on the surface of the blocks, resistant to reactive gases. However, the resistance of the anode layer is affected by many factors in particular related to the microstructure of the product (grain size, phase precipitation, porosity) and it is always desirable to improve this parameter.

Lastly, as for any industrial process, it is desirable to obtain the targeted properties via an economic process. Large scale development of vacuum chambers for many mass-marketed applications (flat screens, solar panels) has recently led to increased interest in simplifying the manufacturing processes.

U.S. Pat. No. 6,565,984 (Applied Materials Inc.) describes an alloy suitable for the manufacture of chambers for the manufacture of semiconductors composed as follows (in weight %): Si: 0.54-0.74, Cu: 0.15-0.30; Fe: 0.05-0.20; Mn≦0.14; Zn≦0.15; Cr: 0.16-0.28; Ti≦0.06; Mg: 0.9-1.1. The parts are obtained by extrusion or machining to reach the required shape. The composition makes it possible to check the size of the impurity particles which improves the performance of the anode layer.

U.S. Pat. No. 6,982,121 (Kyushyu Mitsui Aluminum) describes an alloy suitable for anodizing and suitable for plasma treatment chambers, containing (in weight %): Mg: 2.0 to 3.5; Ti: 0.004 to 0.01% and the rest aluminum, 99.9% pure. The alloy does not require heat treatment, unlike alloys requiring the precipitation of Mg₂Si. In addition, the alloy does not require the presence of Cr and Mn which must be added to alloys 5052 and 6061 to control the grain size, but which are likely to cause heavy metal pollution of the semiconductors treated. The mechanical characteristics of the alloy are not, however, indicated. In addition the cost of 99.9% pure aluminum is high.

US patent application 2009/0050485 (Kobe Steel, Ltd.) describes an alloy of composed as follows (in weight %): Mg: 0.1-2.0, Si: 0.1-2.0, Mn: 0.1-2.0; Fe, Cr, and Cu≦0.03, anodized so that the hardness of the anode oxide coating varies throughout the thickness. The very low iron, chromium and copper content leads to a high excess cost for the metal used.

Patent applications US 2001/019777 and JP2001 220637 (Kobe Steel) describe an alloy for chambers comprising (in weight %) Si: 0.1-2.0, Mg: 0.1-3.5, Cu: 0.02-4.0 and impurities, the Cr content being less than 0.04%.

Patent application EP 2 003 219 A2 (Kobe Steel) describes a forging alloy comprising (in weight %) Mg 0.5-1.25%, Si: 0.4-1.4%, Cu: 0.01-0.7%, Fe: 0.05-0.4%, Mn: 0.001-1.0%, Cr 0.01-0.35%, Ti et Zr 0.005-0.1%. This document discloses in particular products obtained by carrying out before solution heat treatment a hot forging step.

The document “The effect of processing and Mn content on the T5 and T6 properties of AA6082 profiles”, Journal of Materials Processing Technology, 173 (2006) 84-91 describes profiles in alloy AA6082. This document discloses in particular products obtained by carrying out before solution heat treatment a hot extruding step.

The processes used in these documents lead to a high cost (because of the purity of the aluminum used, and the many steps involved in the process). There is a need for an improved and inexpensive process for the manufacture of aluminum alloy blocks designed to be used in the production of vacuum chambers, with high mechanical characteristics, low residual stresses and allowing, after machining, the formation of anode layers resistant to reactive gases.

SUBJECT OF THE INVENTION

A first subject of the invention is a manufacturing process for a block of aluminum at least 250 mm thick designed for the manufacture of elements for vacuum chambers wherein the following operations are carried out successively:

(a) an alloy block with a composition in weight % Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other elements<0.05 each and <0.15 in total, the rest aluminum is cast by semi-continuous casting; (b) optionally, the cast block is homogenized at a temperature ranging between 500° C. and 590° C.; (c) solution heat treatment is performed at a temperature ranging between 450 and 560° C. directly on the cast and optionally homogenized block; without carrying out before solution heat treatment a hot or cold working step, (d) the block that has undergone solution heat treatment is quenched at a cooling speed between the solution heat treatment temperature and 200° C. of at least 200° C./h; (e) optionally the block quenched in this way can be stress-relieved; (f) the block quenched and optionally stress-relieved is artificially aged.

Another subject of the invention is a block composed as follows (in weight %): Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other elements<0.05 each and <0.15 in total, the rest aluminum, at least 250 mm thick, and, in T6 or T652 temper, with a ultimate tensile strength Rn, at ¼ thickness of at least 280 MPa and an tensile yield strength R_(p0.2) at ¼ thickness of at least 240 MPa, obtained by semi-continuous casting, optionally homogenizing at a temperature ranging between 500° C. and 590° C., solution heat treating at a temperature ranging between 450° C. and 560° C. directly on the cast and optionally homogenized block, without carrying out before solution heat treatment a hot or cold working step, quenching with a cooling speed between the solution heat treatment temperature and 200° C. of at least 200° C./h, optionally stress-relieving and artificial aging.

Yet another subject of the invention is the use of a block according to the invention in the production of vacuum chambers for the manufacture of integrated electronic circuits containing semiconductors, flat screens and/or photovoltaic panels.

DESCRIPTION OF THE FIGURES

FIG. 1: Granular structure of the blocks obtained by the process according to invention 11 (FIG. 1 a) and 21 (FIG. 1 b).

FIG. 2: Granular structure of the block reference 31 (FIG. 2 a) and of the block obtained by a process according to prior art (working by forging before solution heat treatment) (FIG. 2 b).

DETAILED DESCRIPTION OF THE INVENTION

The designation of alloys is compliant with the rules of The Aluminum Association (AA), known to those skilled in the art. The definitions of the metallurgical tempers are indicated in European standard EN 515.

Unless otherwise stated, the static mechanical characteristics, in other words the ultimate tensile strength Rm, the conventional tensile yield strength at 0.2% of elongation Rp 0.2 and elongation at rupture A %, are determined by a tensile test according to standard EN 10002-1, sampling and test direction being defined by standard EN 485-1. Hardness is measured according to standard EN ISO 6506.

The parts for vacuum chambers are in particular vacuum chamber bodies, valve bodies, flanges, connecting elements, sealing elements, passages, and flexible pipes. In the process according to the invention, an alloy of the 6xxx family is transformed into a block that can be used for the production of parts for vacuum chambers without hot or cold working before solution heat treatment. So according to the invention, a block at least 250 mm thick made of an alloy, composed as follows (in weight %): Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other elements<0.05 each and <0.15 in total, the rest aluminum, is obtained by semi-continuous casting, optionally homogenizing the cast block at a temperature ranging between 500° C. and 590° C.; solution heat treating at a temperature ranging between 450 and 560° C. directly on the cast and optionally homogenized, without carrying out before solution heat treatment a hot or cold working step, block; quenching with a cooling speed between the temperature of solution heat treatment and 200° C. of at least 200° C./h; optionally stress-relieving and aging. Solution heat treatment directly on the cast block, without carrying out before solution heat treatment a hot or cold working step, is, within the scope of this invention, taken to mean that there is no hot or cold working step before the solution heat treatment. However, conventional steps such as surface machining or sawing an end may be performed, in particular before or after homogenization. The iron content must be lower than 0.3 wt. % because above this figure the anode layer obtained to protect the metal from reactive gases does not reach the required resistance. The present inventors did, however, note that it is not necessary to reach a very high level of purity to obtain anode layers displaying the required characteristics using the process according to the invention. The iron content is therefore advantageously at least 0.1 wt. %, which makes the process according to the invention particularly economical.

The copper content must be lower than 0.2 wt. % because too high a copper content increases quench sensitivity. It is however advantageous in certain cases to add a limited amount of copper to improve the mechanical characteristics, in particular when the cooling speed after solution heat treatment is greater than 800° C./h. A copper content ranging between 0.03 and 0.15 wt. % is preferred in one embodiment of the invention.

The present inventors noted that if the chromium content is not lower than 0.10 wt. %, the required mechanical properties, in particular the minimal mechanical resistance, are not obtained. It is commonly accepted that to produce a wrought product for a vacuum chamber made of 6xxx family alloy the presence of chromium and/or manganese is necessary in order to control the grain size. The present inventors noted that, within the scope of this invention, the absence of chromium is, on the contrary, favorable because without damaging the granular structure it makes it possible to limit quench sensitivity and to improve the mechanical characteristics of thick products. In an advantageous embodiment of the invention, the chromium content is lower than 0.05 wt. % and preferably lower than 0.03 wt. %. The manganese content must be lower than 0.8 wt. %, a content higher than 0.8 wt. % being detrimental, in particular with regard to the properties of the anode layer and contamination of the vacuum chamber. Advantageously the manganese content is lower than 0.6 wt. % to avoid the formation of coarse phases that may be detrimental to the properties of the anode layer. In an advantageous embodiment of the invention, the manganese content is even lower than 0.05 wt. %. The present inventors noted that, surprisingly, even in the absence of Cr, Mn and Zr, the granular structure obtained by the process according to the invention is controlled and makes it possible to obtain satisfactory characteristics in terms of mechanical properties and resistance to reactive gases. The simultaneous absence of Cr, Mn and Zr therefore makes it possible to very significantly decrease the alloy's quench sensitivity and therefore to improve the mechanical properties of thick products, without detriment to the granular characteristics and the properties of the anode layers. In an advantageous embodiment of the invention, the Cr, Mn and Zr contents are simultaneously lower than 0.05 wt. % and preferably lower than 0.03 wt. %.

The silicon and magnesium contents are between 0.5 and 1.5 wt. %. Advantageously, either the combination of 0.5 to 0.8 wt. % of silicon with 0.8 to 1.2 wt. % of magnesium, or the combination of 0.8 to 1.2 wt. % of silicon with 0.6 to 1.0 wt. % of magnesium is used. In a preferred embodiment of the invention making it possible to obtain particularly high mechanical characteristics, the silicon content ranges between 0.8 and 1 wt. %, and preferably between 0.85 and 0.95 wt. %, and the magnesium content ranges between 0.6 and 0.8 wt. % and preferably between 0.65 and 0.75 wt. %.

The alloy is cast using the direct chill casting process in the form of a block. Typically, a block format of between 300 and 450 mm thick is used.

The cast block may, optionally, be homogenized at a temperature ranging between 500° C. and 590° C. for at least one hour. Performing homogenization is advantageous because it generally makes it possible to obtain more advantageous mechanical properties and better properties of the anode layer, and in addition to reduce the length of solution heat treatment. The homogenization can be carried out during a separate heat treatment operation or alternatively during the solution heat treatment.

Between casting and solution heat treating, before or after homogenization when performed, surface machining is generally performed, of approximately at least 5 mm per face, in order to eliminate the segregated surface layer and prevent cracking.

Solution heat treatment is then performed directly on the cast and optionally, homogenized block at a temperature ranging between 450 and 560° C., and preferably between 520 and 550° C. directly, without any hot or cold working step beforehand. Hot working, conventionally one of the processes of prior art, is in general carried out by rolling and/or forging and/or extruding. Thus the block does not undergo between casting and solution heat treating any significant working step. By working it is understood typically operations of rolling and/or forging and/or extruding. Thus, according to the invention, none of the dimensions of the cast block (length, width, thickness) undergoes a significant change, that is typically of at least 10% by working between cast and solution heat treatment. The duration of solution heat treatment is preferably greater than one hour. The process according to the invention, which makes it possible to avoid hot or cold working before solution heat treatment, is particularly advantageous from an economic point of view because this step is an expensive one. According to prior art, this type of process had not been considered, especially for blocks designed for the production of elements for vacuum chambers made of 6xxx alloy, probably because it was feared that, without hot working, the mechanical characteristics, the resistance of the anode layers and the level of porosity, necessary to manufacture elements for vacuum chamber, would not be obtained. In addition, certain particularly thick products were not accessible using the processes according to prior art. Surprisingly, the present inventors noted that the process simplified in this way not only makes it possible to obtain properties equivalent to those obtained by the process according to prior art, but in certain cases to improve upon them.

After solution heat treatment, the quenching step is critical, and must be performed with a cooling speed between the temperature of solution heat treatment and 200° C. of at least 200° C./h. The cooling speed is calculated midway through the thickness of the blocks. If the cooling speed is too low, the present inventors noted that the required mechanical properties are not obtained.

In a first advantageous embodiment of the invention, the cooling speed ranges between 200° C./h and 400° C./h. Surprisingly, when the cooling speed lies between 200° C./h and 400° C./h, satisfactory mechanical characteristics and low residual heat are simultaneously obtained making it possible to avoid the step of stress-relieving by compression. Such a cooling speed can be obtained by mist spraying.

In a second advantageous embodiment of the invention, the cooling speed is at least equal to 800° C./h. Such a cooling speed can be obtained by sprinkling or immersing in water. Since too high a cooling speed may generate too great internal stresses in the blocks, water at a temperature of at least 50° C. is preferably used for cooling.

Optionally, the block quenched in this way is stress-relieved, preferably by cold compression with permanent set ranging between 1% and 5%. In the second embodiment for which the cooling speed is greater than 800° C./h, stress-relieving proves to be particularly advantageous. Stress-relieving makes it possible to decrease the residual stresses in the metal and to avoid bending during machining.

Finally, the block quenched and optionally stress-relieved is artificially aged. The aging temperature preferably lies between 150 and 190° C. and preferably between 165 and 185° C., the duration of aging ranging between 5 and 40 hours and preferably between 8 and 20 hours. Advantageously, aging is performed to reach T6 or T652 temper, corresponding to the peak of the static mechanical properties (Rn, and R_(p0.2)).

The blocks obtained by the process according to the invention are characterized by high mechanical properties. Ultimate tensile strength R_(m) at ¼ of the thickness of the products obtained by the process according to the invention is at least 280 MPa and the tensile yield strength R_(p0.2) at ¼ of the thickness is at least 240 MPa in temper T6 or T652. In an advantageous embodiment, an alloy is used composed as follows: Si: 0.5-1.2, Mg: 0.6-1.0; Fe 0.1-0.3; Cu<0.2; Mn<0.05; Cr<0.05; Ti<0.15; other elements <0.05 each <0.15 in total, and in temper T6 or T652 a ultimate tensile strength R_(m) at ¼ of the thickness of at least 300 MPa and an tensile yield strength R_(p0.2) at ¼ of the thickness of at least 270 MPa are obtained; and in addition if the silicon content lies between 0.8 and 1 wt. % and preferably between 0.85 and 0.95 wt. % and the magnesium content lies between 0.6 and 0.8 wt. % and preferably between 0.65 and 0.75 wt. %, a ultimate tensile strength R_(m) at ¼ of the thickness of at least 320 MPa an tensile yield strength R_(p0.2) at ¼ of the thickness of at least 300 MPa, in temper T6 or T652.

A minimal elongation value of at least 0.5% is obtained by the products according to the invention in temper T6 or T652. In certain cases a minimal elongation value of at least 4% is obtained by the products according to the invention.

The granular structure of the products according to the invention is characteristic of the absence of working before solution heat treatment. It is therefore possible to distinguish the products according to the invention from the products according to prior art for which hot or cold working is performed before solution heat treatment, by a simple metallographic test. Typically, the granular structure of the products according to the invention is isotropic, with an average grain size of at least 200 μm.

The blocks obtained by the process according to the invention are suitable for being used in the production of vacuum chambers for the manufacture of integrated electronic circuits containing semiconductors, flat screens and/or photovoltaic panels. The blocks' behavior with regard to machining is favorable, particularly on account of the high mechanical characteristics and the low level of residual stresses. In addition, the anode layers obtained on the blocks machined by means of the usual anodizing processes are resistant to the reactive gases used in vacuum chambers.

The blocks obtained by the process according to the invention can also be advantageously used for any other application in which the properties obtained are favorable.

Example

In this example the process according to the invention is compared with a process according to reference examples. The process according to the invention was applied to two different alloys.

The direct chill casting process was used to cast four blocks made of an alloy composed as shown in table 1. The blocks were surface-machined down to a thickness of 410 mm

TABLE 1 Composition of alloys tested (wt. %). Alloy Block Si Fe Cu Mn Mg Cr Ti 1 11 0.9 0.13 <0.01 <0.01 0.7 <0.01 0.02 and 12 2 21 1.0 0.23 0.05 0.5 0.8 0.03 0.01 3 31 0.7 0.39 0.24 0.1 1.0 0.19 0.02

The blocks were homogenized at a temperature of between 540 and 590° C. for at least 4 hours.

The blocks then underwent solution heat treatment at 540° C. After solution heat treatment, blocks 11, 21 and 31 were quenched with water at 60° C. (the average cooling speed calculated between 540° C. and 200° C. was approximately 1500° C./h), while block 12 was quenched with air (the average cooling speed between 540° C. and 200° C. was approximately 90° C./h).

The various blocks then underwent cold compression from 1.5 to 2.5% and subsequently underwent aging at 165° C. in order to obtain temper T652.

The granular structure of the products obtained is shown in FIGS. 1 a (block 11), 1 b (block 21) and 2 a (block 31). For purposes of comparison, the granular structure of a product using a process according to prior art (forging before solution heat treatment) is shown in FIG. 2 b. The mechanical characteristics obtained are given in table 2

TABLE 2 mechanical characteristics obtained (T652 temper) after sampling at ¼ thickness in direction TL. Rm Rp0.2 Hardness (MPa) (MPa) A (%) HB 11 (Inv) 334 315 1 109 21 (Inv) 287 245 5.9 88 31 (Ref) 276 229 6.2 87 12 (Ref) 159 92 16.2

The blocks obtained by the process according to the invention (11 and 21), have a higher mechanical resistance (Rm, Rp0.2) than that obtained with the reference ingots, the mechanical resistance obtained with ingot 11 being particularly advantageous.

The blocks obtained according to the invention had low residual stresses, which makes it possible to avoid block bending during machining. The level of porosity observed in the blocks according to the invention was very low, sufficiently low to obtain a high vacuum. 

1. A Manufacturing process for a block of aluminum at least 250 mm thick designed for manufacture of an element for a vacuum chamber, said process comprising successively: (a) casting an alloy block with a composition in weight % Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other elements <0.05 each and <0.15 in total, the rest aluminum by semi-continuous casting; (b) optionally, homogenizing the cast block at a temperature ranging from 500° C. to 590° C.; (c) performing solution heat treatment at a temperature ranging from 450 to 560° C. directly on the cast and optionally homogenized block; without carrying out before solution heat treatment a hot or cold working step; (d) quenching the block that has undergone solution heat treatment between the solution heat treatment temperature and 200° C. at a cooling speed of at least 200° C./h; (e) optionally stress-relieving the block quenched in this way; (f) artificially aging the block quenched and optionally stress-relieved.
 2. The process according to claim 1, wherein the manganese content is lower than 0.6 wt. % and optionally lower than 0.05 wt. %
 3. The process according to claim 1, wherein the chromium content is lower than 0.05 wt. % and optionally lower than 0.03 wt. %.
 4. The process according to claim 1, wherein the Cr, Mn and Zr contents are simultaneously lower than 0.05 wt. % and optionally lower than 0.03 wt. %.
 5. The process according to claim 1, wherein the iron content is at least 0.1 wt. %.
 6. The process according to claim 1, wherein the silicon content is from 0.5 to 0.8 wt. % and the magnesium content is from 0.8 to 1.2 wt. %.
 7. The process according to claim 1 wherein the silicon content is from 0.8 to 1.2 wt. % and the magnesium content is from 0.6 to 1.0 wt. %.
 8. The process according to claim 7, wherein the silicon content ranges from 0.8 to 1 wt. % and optionally from 0.85 to 0.95 wt. %, and said magnesium content ranges from 0.6 to 0.8 wt. % and optionally from 0.65 0.75 wt. %.
 9. The process according to claim 1, wherein said cooling speed from the temperature of solution heat treatment to 200° C. lies from 200° C./h to 400° C./h.
 10. The process according to claim 1, wherein said cooling speed from the temperature of solution heat treatment to 200° C. is at least 800° C./h.
 11. The process according to claim 1, wherein stress-relieving is carried out by cold compression with permanent set ranging from 1% to 5%.
 12. A block comprising in weight %: Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other elements <0.05 each and <0.15 in total, the rest aluminum, said block being at least 250 mm thick, and, in T6 or T652 temper, with a ultimate tensile strength Rm at ¼ thickness of at least 280 MPa and an tensile yield strength Rp0.2 at ¼ thickness of at least 240 MPa, obtained by semi-continuous casting, optionally homogenizing at a temperature ranging from 500° C. to 590° C., solution heat treating at a temperature ranging from 450° C. to 560° C. directly on a cast and optionally homogenized block, without carrying out before solution heat treatment a hot or cold working step, quenching with a cooling speed from the solution heat treatment temperature to 200° C. of at least 200° C./h, optionally stress-relieving and artificial aging.
 13. Block obtained by the process according to of claim
 1. 14. The block according to claim 12, wherein the composition is, in weight %, Si: 0.5-1.2; Mg: 0.6-1.0; Fe 0.1-0.3; Cu<0.2; Mn<0.05; Cr<0.05; Ti<0.15; other elements <0.05 each and <0.15 in total, and in that in temper T6 or T652 said block comprises an ultimate tensile strength Rm at ¼ thickness of at least 300 MPa and a tensile yield strength Rp0.2 at ¼ thickness of at least 270 MPa.
 15. The block according to claim 12, capable of being used in producing a vacuum chamber for manufacture of an integrated electronic circuit containing a semiconductor, a flat screen and/or a photovoltaic panel.
 16. The process according to claim 2, wherein the chromium content is lower than 0.05 wt. % and optionally lower than 0.03 wt. %.
 17. The block according to claim 13, wherein the composition is, in weight %, Si: 0.5-1.2; Mg: 0.6-1.0; Fe 0.1-0.3; Cu<0.2; Mn<0.05; Cr<0.05; Ti<0.15; other elements <0.05 each and <0.15 in total, and in that in temper T6 or T652 the block has an ultimate tensile strength Rm at ¼ thickness of at least 300 MPa and a tensile yield strength Rp0.2 at ¼ thickness of at least 270 MPa. 